Water flooding as an oil recovery technique has been in use since 1890 when operators in the US realised that water entering the productive reservoir formation was stimulating production. In some cases, water is supplied from an adjacently connected aquifer to push the oil towards the producing wells. In situations where there is no aquifer support, water must be pumped into the reservoir through dedicated injection wells. The water phase replaces the oil and gas in the reservoir and thereby serves to maintain pressure. Recovery factors from water flooding vary from 1-2% in heavy oil reservoirs up to 50% with typically values around 30-35%, compared to 5-10% obtained from primary depletion without water flooding.
Large volumes of water are used in water flooding so the water source is typically seawater. Certain naturally occurring elements, compounds, minerals, ions, and bacteria as well as organic pollutants, phosphate pollutants, nitrates, sulfates, and other pollutants from detergent use, pesticide use and fertilizer use may end up in the water source used for water flooding. It is not desirable for these water contaminants to be contacted with crude oil mixtures. These water “contaminants” can lead to or catalyze various chemical reactions with the oil, or with the containers and oil pipes, such as oxidation, hydrogenation, addition or elimination reactions. Furthermore, these “contaminants”/analytes can negatively impact the oil recovery process by affecting the capacity of the water to create emulsions and to penetrate the reservoir rock. The impact of these water contaminants/analytes can lead to lower grade oil product, reduced oil recovery, reduced efficacy of linked-polymer solution or related processes, and reduced life time of machinery, due to corrosion of piping and other equipment. It is therefore desirable to remove analytes from the water source before its use in oil recovery processes.
Currently, ions, salts, elements, minerals and other analytes are removed from injection water by various processes, such as reverse osmosis, filtration, including nano-filtration, vapour distillation and freezing desalination. The removal of bacteria, particularly sulphate reducing bacteria, from water sources used for water flooding is similarly advantageous. Various techniques are currently used for removal of these bacteria from water sources, including ultraviolet light and biocides. Sulfate-reducing bacteria (SRB) are bacteria present in seawater used for waterflooding which have the unfortunate effect of producing hydrogen sulfide (H2S) that cause corrosion of oil platform facility equipment. Additionally bacteria can form so-called biofilms on metal surfaces leading to damage of the equipment.
Corrosion of pipelines is a major concern for the oil industry. Over the past two decades, it has become clear that corrosion in water injection pipelines is to a large extent caused by H2S-producing bacteria; this phenomenon is commonly referred to as microbially-induced corrosion (MIC). The bacteria responsible for corrosion belong to a group of sulphate-reducing bacteria (SRB), which are active under anaerobic conditions.